Adenanthos sericeus

''Adenanthos sericeus'', commonly known as woolly bush, is a shrub native to the south coast of Western Australia. It has bright red but small and obscure flowers, and very soft, deeply divided, hairy leaves.

Description

''Adenanthos sericeus'' mostly grows as an upright, spreading shrub but occasionally takes the habit of a small tree up to 5 m (16 ft) tall. It has erect branches that are covered in short hairs when young, but these are lost with age. Leaves may be up to 40 mm (1.6 in) long, and repeatedly divide by threes into from 5 to 50 narrow laciniae, circular in cross-section, with a diameter of less than 0.5 mm (0.02 in).

Flowers are red, and occur alone or in small groups, hidden within the foliage at the end of branches. As with most other Proteaceae, each flower is composed of a tubular perianth of four united tepals, ending in a structure called a ''limb''; and a single pistil, the stigma of which is initially trapped inside the limb, but is released at anthesis. In ''A. sericeus'', the perianth is bright red, about 28 mm (1.1 in) long, hairy on the outside but smooth and hairless inside. The style is about 40 mm (1.6 in) long; being much longer than the perianth, it is very sharply bent for as long as the stigma remains trapped within the limb, and then springs erect. The fruit is an oval-shaped achene about 5 mm (0.2 in) long.

Taxonomy

Discovery and naming

This species was first described by Jacques Labillardière in his 1805 '' Novae Hollandiae Plantarum Specimen'', under the name ''Adenanthos sericea''. No explicit etymology for the specific name was given, but it is accepted that it is from the Latin ''sericeus'' ("silky"), in reference to the very soft foliage.

Labillardière did not acknowledge any collector, and so it was long thought that Labillardière himself has collected the first botanical specimens. This was not obviously problematic, as ''A. sericeus'' does occur at Esperance Bay, where Labillardière collected in December 1792. However, several Australian plant species described by Labillardière do not occur in any locations that he visited, suggesting that some of his specimens were obtained from some other collector whom he failed to credit. This prompted a re-evaluation of the type material by Ernest Charles Nelson, who found several items of evidence suggesting that Labillardière could not have collected the specimens that he apparently used to describe the species:
* The specimens are labelled as having come from the herbarium of René Louiche Desfontaines, not that of Labillardière
* The specimens belong to the King George Sound form of the species (since published as ''A. sericeus'' subsp. ''sericeus''), which Labillardière could not have collected; whereas the Esperance Bay populations of this species belong to a distinctively different form (since published as ''A. sericeus'' subsp. ''sphalma'').
* Present-day Esperance Bay populations of ''A. sericeus'' are restricted to the granitic soils of Cape Le Grand at the extreme east of Esperance Bay, whereas Labillardière collected only in the vicinity of Observatory Island and Observatory Point, 30 km (20 mi) west of Cape Le Grand at the extreme west of Esperance Bay, where the soils are not of granitic origin.
Nelson concluded that Labillardière could not have collected this species, instead attributing collection to Jean Baptiste Leschenault de la Tour, who visited King George Sound in 1803 as a member of Nicolas Baudin's voyage of exploration. This view has been accepted by some scholars though others treat it more cautiously.

Infrageneric placement

In 1870, George Bentham published the first infrageneric arrangement of ''Adenanthos'' in Volume 5 of his landmark '' Flora Australiensis''. Bentham divided the genus into two sections, placing ''A. sericea'' in ''A.'' sect. ''Stenolaema'' because its perianth tube is straight and not swollen above the middle. This arrangement still stands today, though ''A.'' sect. ''Stenolaema'' is now renamed to the autonym ''A.'' sect. ''Adenanthos''. Bentham also published a variety, ''A. sericea'' var. ''brevifolia'' (now '' A. macropodianus'') based on specimens collected from Kangaroo Island in South Australia.

This broad view of ''A. sericea'' continued into the 20th century, with several other species included in it, including '' A. oreophila'' and '' A. cygnorum''. The current, narrower circumscription originated with Nelson's 1970 investigation of ''Adenanthos''. Nelson was interested in the problem of why there are so many plant species with disjunct distribution patterns in southern Australia. One such species was ''A. sericea'', the Kangaroo Island form of which occurred about 2500 km (1600 mi) east of the nearest population of the Western Australian variety. This led Nelson to undertake a full taxonomic revision of ''Adenanthos'', in the course of which he concluded that the Kangaroo Island form of ''A. sericea'' warranted species rank, primarily because leaves are much smaller and have fewer laciniae than the Western Australian ''A. sericea''. In 1978 he published ''A. macropodiana'' and synonymized ''A. sericea'' var. ''brevifolia'' with it. He also published ''A. oreophila'' and clarified confusion between ''A. sericea'' and ''A. cygnorum''. Finally, Nelson refined Bentham's arrangement by dividing ''A.'' sect. ''Adenanthos'' into two subsections, with ''A. sericea'' placed into ''A.'' subsect. ''Adenanthos'' for reasons including the length of its perianth. However Nelson discarded his own subsections in his 1995 treatment of ''Adenanthos'' for the '' Flora of Australia'' series of monographs. By this time, the ICBN had issued a ruling that all genera ending in ''-anthos'' must be treated as having masculine gender; thus the specific epithet became ''sericeus''.

The placement of ''A. sericeus'' in Nelson's arrangement of ''Adenanthos'' may be summarised as follows:
:''Adenanthos''
:: ''A.'' sect. ''Eurylaema'' (4 species)
:: ''A.'' sect. ''Adenanthos''
:::'' A. drummondii''
:::'' A. dobagii''
:::'' A. apiculatus''
:::'' A. linearis''
:::'' A. pungens'' (2 subspecies)
:::'' A. gracilipes''
:::'' A. venosus''
:::'' A. dobsonii''
:::'' A. glabrescens'' (2 subspecies)
:::'' A. ellipticus''
:::'' A. cuneatus''
:::'' A. stictus''
:::'' A. ileticos''
:::'' A. forrestii''
:::'' A. eyrei''
:::'' A. cacomorphus''
:::'' A. flavidiflorus''
:::'' A. argyreus''
:::'' A. macropodianus''
:::'' A. terminalis''
:::''A. sericeus''
:::: ''A. sericeus'' subsp. ''sericeus''
:::: ''A. sericeus'' subsp. ''sphalma''
:::'' A. × cunninghamii''
:::'' A. oreophilus''
:::'' A. cygnorum'' (2 subspecies)
:::'' A. meisneri''
:::'' A. velutinus''
:::'' A. filifolius''
:::'' A. labillardierei''
:::'' A. acanthophyllus''

Subspecies and hybrids

Two subspecies are recognised:
* ''A. sericeus'' subsp. ''sericeus'' is an autonym that encompasses the populations around King George Sound. The leaves of this subspecies are typically over 30 mm (1.2 in) long, and divided into many laciniae: average numbers range from 11 to 35, but individual leaves may have up to 50.
* ''A. sericeus'' subsp. ''sphalma'' encompasses the populations at Cape Le Grand, which have smaller leaves typically divided into around 6 laciniae, and rarely more than 12. The existence of two subspecies was recognised by Nelson as early as 1975, but because of the confusion surrounding the type collection, Nelson treated this subspecies as encompassing the type material and therefore treated it as the autonymic subspecies. This error appeared in his doctoral thesis and on herbarium specimens annotations made by Nelson before 1977. This explains the subspecific epithet ''sphalma'', from the Latin ''sphalmus'' ("mistake").

''Adenanthos'' × ''cunninghamii'' is considered a hybrid between ''A. sericeus'' subsp. ''sericeus'' and '' A. cuneatus''. It occurs in Torndirrup National Park and sometimes at Two Peoples Bay, and back-crosses with ''A. cuneatus'' have also been found in the vicinity of King George Sound. It can be distinguished from ''A. sericeus'' by its duller flowers, and by its foliage, which has very thick laciniae and, like, ''A. cuneatus'', red new growth.

Common names

Common names for ''A. sericeus'' include '' Woollybush''—a name applied to all ''Adenanthos'' species with deeply divided foliage—and various qualifications of this, including ''Coastal Woollybush'', ''Tall Woollybush'', and ''Albany Woollybush''. However the last of these also refers to ''A.'' × ''cunninghamii'', and Nelson has referred to it as " name... so confused it is now almost useless." In the cut flower industry, which values its silvery foliage, the common names ''Smoke Bush'' and ''Australian Smoke Bush'' have also been used.

In Australian nurseries, it is sold under the name ''Silver Streak'' as a popular hedge plant for domestic gardens and landscaping.

Distribution and habitat

''Adenanthos sericeus'' has a disjunct distribution spanning about 500 km (300 mi) of the south coast of Western Australia. ''A. sericeus'' subsp. ''sericeus'' occurs mostly around King George Sound, extending west as far as Torbay Inlet and east almost to Cape Riche; it sometimes occurs very close to the sea. There is then a gap of over 300 km (200 mi) to the populations of ''A. sericeus'' subsp. ''sphalma'' at Cape Le Grand. Another group of ''A. sericeus'' subsp. ''sphalma'' occurs 100 km (60 mi) further east at Cape Arid.

Both subspecies are calcifuge, occurring only in siliceous sands derived from weathered granite. Thus most populations are associated with granite monadnocks. Though its range is restricted, it is locally common and often dominant. ''A. sericeus'' subsp. ''sphalma'' is often found in association with ''Nuytsia floribunda'', '' Kunzea baxteri'', and '' Xanthorrhoea'' species.

Ecology

Both subspecies flower throughout the year, though ''A. sericeus'' subsp. ''sphalma'' flowers most between August and December.

It is susceptible to '' Phytophthora cinnamomi'' dieback.

Cultivation

Though its flowers are inconspicuous, ''A. sericeus'' is considered an attractive garden plant for the colour and texture of its dense foliage. Its high tolerance of salt-laden winds makes it an excellent screen plant in coastal areas. In the Albany area, branches or entire potted plants are used as Christmas trees, since young plants are shaped like small pine trees but have a silky feel. One study of application of controlled-release fertiliser to ''A. sericeus'' in pots found it benefited from increasing levels of fertiliser, whereas other species plateaued at lower levels.
Propagation is by cuttings. These strike readily, but care must be taken not to mist the foliage too much, or it will rot. It requires very good drainage, and performs poorly in humid areas. Lacking a lignotuber, it tolerates only light pruning.

Several cultivars have become available, including two developed and propagated in Israel.

The silvery foliage is used commercially in the cut flower industry. It has an unusually long vase life: tests have yielded a vase life of 30 days, regardless of treatment or time of year.

References

External links

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{{Taxonbar, from=Q550566

sericeus
Endemic flora of Western Australia
Eudicots of Western Australia
Garden plants of Australia